Britain accused Russia of committing "war crimes" in Syria as world powers rounded on Moscow last night (Sunday night) in one of the most bitter meetings of the UN Security Council in recent memory.
As Russian jets took part in what rebels called the "scorched earth bombing" of Aleppo, Western powers charged Vladimir Putin, the Russian president, with deliberately undermining peace talks and flouting its historic responsibilities to the United Nations.
The almost complete rupture of relations between Russia and the Western powers played out in angry scenes at the UN's New York headquarters, where Britain, France and the US openly condemned Russia as "an international pariah".
The exchanges marked the effective collapse of the US-led Syria peace process that had tried to get to Russia to use its influence in Syria to help bring an end to the six-year war that has now claimed around 400,000 lives.
With a US-backed no-fly zone and other military intervention ruled out by President Obama, Britain, France and the US launched the diplomatic onslaught in an attempt to shame Russia into helping to end the suffering.
Ban Ki-moon, the UN Secretary-General, urged the powers to work to "end the nightmare" singling out Russia's use of bunker-busting bombs to hit schools and hospitals operating in basements. "How much longer will all those with influence allow such cruelty to continue?" Mr Ban said.
Earlier, Boris Johnson, the British Foreign Secretary, said Russia may have committed war crimes by bombing a UN aid convoy last week and accused President Putin of not only "handing the revolver" to the Assad regime, but also helping to pull the trigger.
In a display of disgust towards the Assad regime, Matthew Rycroft, the British ambassador to the UN, walked out of a specially convened Security Council meeting when the Syrian ambassador rose to speak.
"Aleppo's inhabitants... are now facing an unprecedented, unrelenting onslaught of cruelty," he said. "In short, it is difficult to deny that Russia is partnering with the Syrian regime to carry out war crimes."
Mr Rycroft also hinted that Western powers must now consider coercive measures to force Russia to back away. "We must now do more than demand or urge. We must now decide what we can do to enforce end to bombardment," he said, without providing details. The West could now consider economic sanctions or a diplomatic move against Russia to try to force it to change course.
Russia denied the Western charges and accused Western-backed rebel groups of causing the breakdown of the ceasefire.
Samantha Power, the US ambassador to the UN, said Russian forces were guilty of "barbarism" for using bunker-busting bombs. "Russia would have this Council live in upside-down land where bombing first responders, cutting off humanitarian aid and supporting a murderous regime is billed as counterterrorism," she said. "What Russia is sponsoring and doing is not counterterrorism; it is barbarism."